Indole derivatives and their use

ABSTRACT

Indole derivatives of formula (I) ##STR1## wherein R 1 , R 2 , R 3  and R 4  may be hydrogen or lower alkyl optionally substituted by halogen; A 1  represents a straight or branched alkylene chain containing from 2 to 4 carbon atoms; R 5  is hydrogen or a straight or branched alkyl group; A 2  is a straight or branched, saturated or unsaturated hydrocarbon chain containing from 2 to 6 carbon atoms; and R 6  is selected from a group consisting of various structures, have been found to exhibit central nervous system activities.

This invention is in the field of pharmaceutical agents exhibiting central nervous system (CNS) activities. More specifically, the invention relates to novel indole derivatives, to a process for their preparation, to pharmaceutical compositions comprising the compounds, and to methods of treating therewith. The novel indole derivatives are potentially suitable for counteracting (including preventing, relieving and curing) certain CNS disorders.

It has long been known that serotonin (5-hydroxy-tryptamine, hereinafter referred to as 5-HT) is a neurotransmitter in the central nervous system. In particular, over the last decade intensive pharmacological research directed to serotonergic neurotransmitter functions has taken place. It is now generally accepted that in the CNS there are at least five different subtypes of 5-HT binding sites or receptors, which types are identifiable as 5-HT_(1A), 5- HT_(1B), 5-HT_(1C), 5-H₂ and 5-HT₃, respectively. Differentiation of the 5-HT receptor subtypes is mainly based on their binding characteristics as characterized by specific radio ligands. For example, the ligand 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) binds with high affinity to 5-HT_(1A) receptors, while another ligand, a 2,4(1H,3H)-quinazolinedione derivative (adopted name: ketanserin) exhibits high affinity for the 5-HT₂ receptor subtype. It is worth noting that none of these synthetic ligands have any chemical resemblance whatsoever to the physiological binding partner, i.e. 5-HT. For a recent review of 5-HT receptor- ligand interactions reference is made to J.R. Fozard: Trends in Pharmacol. Sci. 8 (1987), 501-506.

A variety of indole derivatives which are chemically closer related to 5-HT, such as RU 24969, which is a 3-(tetrahydropyridin-4-yl)-indole (Ann.Reports Med.Chem. 21 (1986), 42-43) have high affinity for 5-HT₁ recognition sites, but generally they show only limited capacity to discriminate between the 5-HT_(1A) and 5-HT_(1B) receptor subtypes.

It has now surprisingly been observed that compounds of the general formula (I) hereinafter bind with high affinity to 5-HT receptors and, furthermore, that some of the compounds exhibit substantially higher affinity for the 5-HT_(1A) subtype than many of the synthetic ligands known heretofore. Based on their binding specificity these compounds may be classified as extremely potent and specific 5-HT_(1A) agonists and, as such, of potential utility for the treatment of disorders associated with serotonergic dysfunctions. Such dysfunctions may be involved in the impairment of thermoregulation, memory function, sleep and satiety control of the consumption of feed and/or beverage, which may include alcohol. They may also play a role in the development of hypertension, hyperemesis, and of such mental states as depression, anxiety or psychosis.

Thus the present invention provides novel indole derivatives of the general formula (I): ##STR2## wherein R¹, R², R³ and R⁴, which may be the same or different, each is selected from the group consisting of hydrogen; lower alkyl containing from 1 to 4 carbon atoms, in which one or more hydrogen atoms may be substituted by halogen, e.g. CF₃ ; OR⁷ or --COOR⁷ in which R⁷ is hydrogen, C₁₋₄ aryl or aralkyl; halogen, e.g. chlorine; and the group ##STR3## wherein R⁸ and R⁹ may be the same or different, each representing hydrogen or lower alkyl containing from 1 to 4 carbon atoms; A¹ represents a straight or branched alkylene chain containing from 2 to 4 carbon atoms; R⁵ is hydrogen or a straight or branched C₁₋₅ -alkyl group; A² is a straight or branched saturated or unsaturated hydrocarbon chain containing from 2 to 6 carbon atoms; and R⁶ is selected from the group consisting of ##STR4## wherein R¹⁰ and R¹¹, which may be the same or different, each represents a C₁₋₃ -alkyl group, or R¹⁰ and R¹¹ together represent a tetra- or pentamethylene chain, thereby forming together with the heterocyclic ring an azaspiro- decanedione/trione or -undecanedione/trione ring structure; ##STR5## wherein R¹² and R¹³ , which may be the same or different, each represents a C₁₋₃ -alkyl group, or R¹² and R¹³ together with their neighbouring carbon atoms form a 5-or 6-membered saturated or nonsaturated ring fused to the 5-membered ring; ##STR6## wherein E is --CH₂ --, --CH₂ --CH₂ --, --CH═CH--, --O-- or --S-- and the dotted line represents optional unsaturation; R¹⁴ and R¹⁵, which may be the same or different, each represents hydrogen, a C₁₋₃ -alkyl group, or R¹⁴ and R¹⁵ together with their neighbouring carbon atoms form a cyclopropane, cyclobutane, cyclobutene, cyclohexane or cyclohexene ring fused to the bicyclic ring structure.

The compounds of formula I may be converted into any physiological acceptable salts thereof.

The invention includes within its scope all optical isomers of compounds of the general formula (I) and their mixtures including racemic mixtures thereof.

Compounds of the general formula (I) were tested for binding to 5-HT receptors and compared with known ligands by the following procedure:

Rat brain tissue (as specified in the table hereinafter) was homogenized using a Polytron homogenizer. The final pellet was resuspended in 125 vol (tissue wet weight) of buffer.

In all assays incubation was carried out for 10 min at 37° C.

Labelling of the 5-HT_(1B) receptor was complicated by the fact that the available ligand ³ H-5-HT is nonselective. However, by inclusion of the 5-HT_(1A) selective agent 8-OH-DPAT in the assay, labelling of the 5-HT_(1A) receptor could be avoided and a relatively selective labelling of the 5-HT_(1B) receptor could be accomplished.

Detailed conditions for the receptor binding assay in vitro are tabulated below.

    __________________________________________________________________________     Receptor type                                                                           5-HT.sub.1A                                                                              5-HT.sub.1B                                                                               5-HT.sub.2                                       __________________________________________________________________________     Ligand   .sup.3 H-80H-DPAT                                                                        .sup.3 H-5-HT                                                                             .sup.3 H-ketanserin                              Tissue   frontal cortex                                                                           frontal cortex                                                                            frontal cortex                                            Hippocampus                                                                              Hippocampus                                                                    striatum                                                    Buffer   50 mM Tris-Citrate                                                                       50 mM Tris-HCl                                                                            50 mM Tris-Citrate                                        (pH 7.4, 30° C.)                                                                  (pH 7.4, 37° C.)                                                                   (pH 7.4, 30° C.)                                   120 mM NaCl,                                                                             120 mM NaCl, 4 mM                                                                         120 mM NaCl, 4 mM                                         4 mM MgCl.sub.2                                                                          CaCl.sub.2, 4mM MgCl.sub.2                                                                MgCl.sub.2                                       Centrifugation                                                                          24,000 × g, twice                                                                  24,000 × g, twice                                                                   24,000 × g, once                           Preincubation                                                                           10 min, 37° C.                                                                    10 min, 37° C.                                                                     --                                               Homogenization                                                                          20 ml     20 ml      20 ml                                            mg tissue/assay                                                                         10        10         10                                               Ligand conc.                                                                            2 nM      1 nM       0.4 nM                                           Addition to assay                                                                       --        50 nM 8-OH-DPAT                                                                           --                                               Monspec. binding                                                                        10 μM serotonin                                                                       10 μM serotonin                                                                        1 μM cyproheptadine                           defined with                                                                   Level of nonspec.                                                                       20-30%    20-25%     12-18%                                           binding                                                                        __________________________________________________________________________

The following results were obtained:

    ______________________________________                                         Receptor binding IC.sub.50 (nM)                                                Compound        5-HT.sub.1A                                                                            5-HT.sub.1B                                            ______________________________________                                         Buspirone       20      above      1000                                        Gepirone        248     above      1000                                        Ipsapirone      25      above      1000                                        8-OH-DPAT       3.4     above      1000                                        Example 1       26                  480                                        Example 2       375                 148                                        Example 4       4       above      1000                                        Example 5       2.5     above      1000                                        ______________________________________                                    

The present invention also provides a process for preparing the compounds of the general formula (I) and physiologically acceptable salts thereof, which process is outlined hereinafter.

A compound of the general formula (II) ##STR7## wherein R¹, R², R³, R⁴, and A¹ are as defined for formula (I), and Z represents R⁵ of formula (I) or a group convertible into hydrogen (during such an akylation process the indole nitrogen and any free hydroxy groups in the benzene ring may be protected, e.g., by benzylation), e.g. benzyl, may be reacted with a compound of the general formula

    L--A.sup.2 --R.sup.6                                       (III)

wherein L represents a leaving group, of which halogen, in particular bromine, is preferred, and A² and R⁶ are defined as in connection with formula (I).

Many representatives of compounds of formula (II) are commercially available or known from the literature. Other compounds falling within the scope of formula (II) may be prepared by methods, which are generally analogous to those of said literature. General methods for the preparation of compounds of formula

    L--A.sup.2 --R.sup.6

are described in British Patent Publication 2,174,703A wherefrom by analogy alternative methods for establishing the ##STR8## chain can be derived.

The reaction may conveniently be effected in an organic solvent, such as an aprotic solvent, e.g. acetonitrile or dimethylformamide in the presence of a base, for example potassium carbonate. When the leaving group L is different from iodine, being e.g. bromine, the reaction can be conducted in the presence of a salt of hydrogen iodide, e.g. potassium iodide. Usually, the reaction is completed with stirring at a temperature above ambient. The reaction product obtained following, if necessary, after the conversion of Z into hydrogen, may be recovered by conventional means and, if desirable, subjected to purification, e.g. by suitable chromatographic procedures.

The purified reaction product may be converted into a physiologically acceptable salt. Such salts include acid addition salts formed with inorganic or organic acids, for example hydrochlorides, hydrobromides, sulphates, nitrates, oxalates, phosphates, tartrates, citrates, fumarates, maleates, succinates, and sulphonates e.g. mesylates.

If desirable, selected salts may be subjected to further purification by recrystallization.

The compound of the invention, together with a conventional adjuvant, carrier, or diluent, and if desired in the form of a pharmaceutically-acceptable acid addition salt thereof, may be placed int the form of pharmaceutical compositions and unit dosages thereof, and in such form may be employed as solids, such as tablets or filled capsules, or liquids, such as solutions, suspensions, emulsions, elixirs, or capsules filled with the same, all for oral use, in the form of suppositories for rectal administration; or in the form of sterile injectable solutions for parenteral (including subcutaneous) use. Such pharmaceutical compositions and unit dosage forms thereof may comprise conventional ingredients in conventional proportions, with or without additional active compounds or principles, and such unit dosage forms may contain any suitable effective central nervous system ailment alleviating amount of the active ingredient commensurate with the intended daily dosage range to be employed. Tablets containing one (1) milligram of active ingredient or, more broadly, one (1) to thirty (30) milligrams, per tablet, are accordingly suitable representative unit dosage forms.

The compounds of this invention can thus be used for the formulation of pharmaceutical preparations, e.g., for oral and parenteral administration to mammals including humans, in accordance with conventional methods of galenic pharmacy.

Conventional excipients are such pharmaceutically acceptable organic or inorganic carrier substances suitable for parenteral or oral application which do not deleteriously react with the active compound.

Examples of such carriers are water, salt solutions, alcohols, polyethylene glycols, polyhydroxyethoxylated castor oil, gelatin, lactose, amylose, magnesium stearate, talc, silicic acid, fatty acid monoglycerides and diglycerides, pentaerythritol fatty acid esters, hydroxymethylcellulose and polyvinylpyrrolidone.

The pharmaceutical preparations can be sterilized and mixed, if desired, with auxilliary agents, such as lubricants, preservatives, stabilizers, wetting agents, emulsifiers, salt for influencing osmotic pressure, buffers and/or coloring substances and the like, which do not deleteriously react with the active compound.

For parenteral application, particularly suitable are injectable solutions or suspensions, preferably aqueous solutions with the active compound dissolved in polyhydroxylated castor oil.

Ampoules are convenient unit dosage forms.

For oral application, particularly suitable are tablets, dragees, or capsules having talc and/or a carbohydrate carrier or binder or the like, the carrier preferably being lactose and/or corn starch and/or potato starch. A syrup, elixir or like can be used when a sweetened vehicle can be employed. Generally, as to broader ranges, the compound of the invention is dispensed in unit dosage form comprising 0.05-100 mg in a pharmaceutically-acceptable carrier per unit dosage.

A typical tablet which may be prepared by conventional tabletting techniques contains:

    ______________________________________                                         Active compound      1.0 mg                                                    Lactosum            67.8 mg Ph.Eur.                                            Avicel              31.4 mg                                                    Amberlite IRP 88     1.0 mg                                                    Magnesii stearas     0.25 mg Ph.Eur.                                           ______________________________________                                    

Due to their high degree of affinity for the 5-HT receptors, the compounds of the invention are extremely useful in the treatment of central nervous system ailments or disorders, when administered in an amount effective for the alleviation, amelioration, or elimination thereof. The important CNS activity of the compounds of the invention as mentioned above, along with a low toxicity, together presenting a most favorable therapeutic index. The compounds of the invention may accordingly be administered to a subject, e.g., a living animal body, including a human, in need of the same for the treatment, alleviation, amelioration, or elimination of an indication, associated with the central nervous system and the 5-HT receptors, which requires such psychopharmaceutical treatment, if desired in the form of a pharmaceutically acceptable acid addition salt thereof (such as the hydrobromide, hydrochloride, or sulfate, in any event prepared in the usual or conventional manner, e.g., evaporation to dryness of the free base in solution together with the acid), ordinarily concurrently, simultaneously, or together with a pharmaceutically-acceptable carrier or diluent, especially and preferably in the form of a pharmaceutical composition thereof, whether by oral, rectal, or parenteral (including subcutaneous) route, in an effective psychopharmaceutical central nervous system ailment alleviating amount, and in any event an amount which is effective for the alleviation of such a central nervous system ailment due to their 5-HT receptor affinity. Suitable dosage ranges are 1-200 milligrams daily, 1-100 milligrams daily, and especially 1-30 milligrams daily, depending as usual upon the exact mode of administration, form in which administered, the indication toward which the administration is directed, the subject involved and the body weight of the subject involved, and the preference and experience of the physician or veterinarian in charge.

The following examples serve to illustrate the present invention.

EXAMPLE 1 1-(4-(1,3-Dioxo-4,7-etheno-1,3,3a,4,4a,6a,7,7a-octahydro-2H-cyclobut[f]isoindol-2-yl)butyl-1-amino)-2-(3-indolyl)-ethane, oxalate

A mixture of tryptamine (480 mg; 3.0 mmol), 2-(4-bromobutyl)-1,3-dioxo-4,7-etheno-1,3,3a,4,4a,6a,7,7a-octahydro-2H-cyclobut[f]isoindole (Abou-Gharbia et al., J.Med.Chem. 1988, 31, 1382-1392) (1.0 g; 3.0 mmol), potassium carbonate (830 mg; 6.0 mmol) in acetonitrile (20 ml) was stirred and heated at 60° C. for 40 h. The solvent was removed under reduced pressure. Ethyl acetate (30 ml) was added to the residue followed by water (30 ml) and the organic phase was separated. The aqueous phase was extracted with ethyl acetate (2×30 ml) and the combined organic phases were dried (MgSO₄), filtered and evaporated to give an oil, which was flash-chromatographed on silica gel 60 with ethyl acetate graduated to ethyl acetate/methanol 4:1. The title compound was isolated as the oxalate. M.p. 209°-210° C. MS (70 eV): m/z 416 (2%, M+1) 415 (2%, M⁺) 285 (100), 256 (7), 214 (4), 130 (27).

EXAMPLE 2 1-(4-Phthalimidobutyl-1-amino)-2-(3-indolyl)-ethane oxalate

A mixture of tryptamine (1.28 g; 8.0 mmol), N-(4-bromobutyl)phthalimide (2.25 g; 8.0 mmol), potassium carbonate (2.2 g; 16 mmol) in acetonitrile (60 ml) was stirred and heated at 60° C. for 40 h. The solvent was removed under reduced pressure. Ethyl acetate (75 ml) was added to the residue followed by water (75 ml) and the organic phase was separated. The aqueous phase was extracted with ethyl acetate (2×75 ml) and the combined organic phases were dried (MgSO₄), filtered and evaporated to give an oil, which was flashchromatographed on silica gel 60 with ethyl acetate. The title compound was isolated as the oxalate. M.p. 215°-218° C. MS (70 eV): m/z 362 (2%, M+1), 361 (1%, M⁺), 231 (100), 202 (8), 160 (30), 130 (31).

EXAMPLE 3 1-(4-(Cis-4-cyclohexen-1,2-dicarboximido)butyl-1-amino)-2-(3-indolyl)-ethane, oxalate

A mixture of tryptamine (620 mg; 3.9 mmol), N-(4-bromoburtyl)-cis-4-cyclohexen-1,2-dicarboximide (1.1 g; 3.9 mmol), potassium carbonate (1.1 g; 8.0 mmol) in acetonitrile (30 ml) was stirred and heated at 60° C. for 40 h. The solvent was removed under reduced pressure. Ethyl acetate (50 ml) was added to the residue followed by water (50 ml) and the organic phase was separated. The aqueous phase was extracted with ethyl acetate (2×50 ml) and the combined organic phases were dried (MgSO₄), filtered and evaporated to give an oil, which was flashchromatographed on silica gel 60 with ethyl acetate. The title compound was isolated as the oxalate. M.p. 166°-167° C. ¹ H NMR (DMSO+D₂ O, 400 MHz) 7.60-6.95 (m, 5H), 5.85 (m, 2H), 3.35 (m, 2H), 3.20-3.10 (m, 4H), 3.10-3.00 (m, 2H), 3.00-2.90 (m, 2H), 2.45-2.10 (m, 4H), 1.50 (m, 4H).

EXAMPLE 4 1-(4-(7,9-Dioxo-8-azaspiro[4,5]decan-8-yl)butyl-1-amino)-2-(5-methoxy-3-indolyl)-ethane, oxalate

A mixture of 5-methoxytryptamine, hydrochloride (500 mg; 2.2 mmol), 8-(4-bromobutyl)-8-azaspiro[4,5]decane-7,9-dione (665 mg; 2.2 mmol), potassium carbonate (550 mg; 40 mmol) in acetonitrile (20 ml) was stirred and heated at 60° C. for 40 h. The solvent was removed under reduced pressure. Ethyl acetate (30 ml) was added to the residue followed by water (30 ml) and the organic phase was separated. The aqueous phase was extracted with ethyl acetate (2×30 ml) and the combined organic phases were dried (MgSO₄), filtered and evaporated to give an oil, which was flashchromatographed on silica gel 60 with ethyl acetate graduated to ethyl acetate/methanol (4:1). The title compound was isolated as the oxalate. M.p. 109.5°-110° C. ¹ H NMR (DMSO+D₂ O, 400 MHz) 7.30-6.70 (m, 4H), 3.75 (s, 3H), 3.60 (m, 2H), 3.15- 3.05 (m, 2H), 3.00-2.90 (m, 4H), 2.60 (s, 4H), 1.65-1.35 (m, 12H).

EXAMPLE 5 1-(4-(1,3-Dioxo-4,7-etheno-1,3,3a,4,4a,6a,7,7a-octahydro-2H-cyclobut[f]isoindol-2-yl)butyl-1-amino)-2-(5-methoxy-3-indolyl)-ethane, oxalate

A mixture of 5-methoxytryptamine, hydrochloride (500 mg; 2.2 mmol), 2-(4-bromobutyl)-1,3-dioxo-4,7-etheno-1,3,3a,4,4a,6a,7,7a-octahydro-2H-cyclobut[f]isoindole (740 mg; 2.2 mmol), potassium carbonate (550 mg; 4.0 mmol) in acetonitrile (20 ml) was stirred and heated at 60° C. for 16 h. The solvent was removed under reduced pressure. Ethyl acetate (30 ml) was added to the residue followed by water (30 ml) and the organic phase was separated. The aqueous phase was extracted with ethyl acetate (2×30 ml) and the combined organic phases were dried (MgSO₄), filtered and evaporated to give an oil, which was flashchromatographed on silica gel 60 with ethyl acetate graduated to ethyl acetate/methanol (4:1). The title compound was isolated as the oxalate. M.p. 122°-123° C. MS (70 eV): m/z 445 (1%, M⁺), 285 (100), 256 (7), 174 (6), 160 (28), 146 (4).

EXAMPLE 6 4-(7,9-Dioxo-8-azaspiro[4,5]decan-8-yl)butyl-2-(5-methoxy-3-indolyl)ethyl-methylamine, oxalate

A mixture of 3-(2-methylaminoethyl)indole (1.0 g, 5.7 mmol), 8-(4-bromobutyl)-8-azaspiro[4,5]decane-7,9-dione (1.7 g, 5.7 mmol) and potassium carbonate (1.4 g, 10 mmol) was stirred and refluxed for 8 h and then concentrated in vacuo. The residue was dissolved in water and extracted with ethyl acetate (three times). The combined organic phases were dried over MgSO₄ and evaporated to give an oil, which was flash chromatographed on silica 60 with ethyl acetate. The product was dissolved in acetone and oxalic acid (500 mg in 5 ml acetone) added to precipitate the desired product. M.p.>80° C., dec. MS (70 eV): m/z 396 (2%, M+1), 395 (M⁺, 1%), 265 (100%), 222 (17%), 180 (5%), 130 (30%). 

We claim:
 1. A compound of formula (I) ##STR9## wherein R¹, R², R³ and R⁴, which may be the same or different, are hydrogen; C₁₋₄ -alkyl, optionally substituted by one or more halogen; --OR⁷ or --COOR⁷ in which R⁷ is hydrogen or C₁₋₄ alkyl; halogen; or the group ##STR10## wherein R⁸ and R⁹, which may be the same or different, are hydrogen or C₁₋₄ -alkyl;A¹ is straight or branched C₂₋₄ -alkylene; A² is straight or branched C₂₋₆ -alkylene; R⁵ is hydrogen or straight or branched C₁₋₅ -alkyl; and R⁶ is ##STR11## wherein E is --CH₂ --, --CH₂ --CH₂ --, --CH═CH--, --O-- or --S--; R¹⁴ and R¹⁵, which may be the same or different, are hydrogen or C₁₋₃ -alkyl, or R¹⁴ and R¹⁵ together with their neighboring carbon atoms form a cyclopropane, cyclobutane, cyclobutene, cyclohexane or cyclohexene ring fused to the bicyclic ring structure; or a pharmaceutically acceptable salt thereof.
 2. A compound according to claim 1 which is 1-(4-(1,3-dioxo-4,7-etheno-1,3,3a,4,4a,6a,7,7a-octahydro-2H-cyclo-but[f]isoindol-2-yl)butyl-1-amino)-2-(5-methoxy-3-indolyl)-ethane, oxalate.
 3. A pharmaceutical composition which comprises at least one compound according to claim 1 or a physiologically acceptable salt thereof and a physiologically compatible carrier or diluent.
 4. A pharmaceutical composition according to claim 3, which comprises between 0.1 mg and 250 mg of the active ingredient or a pharmaceutically acceptable salt thereof per dose unit.
 5. A method of treating a central nervous system ailment associated with serotonergic dysfunctions in a subject in need thereof comprising administering an effective amount of a compound according to claim
 1. 6. A method of treating a central nervous system ailment associated with serotenergic dysfunctions in a subject in need thereof comprising administering a pharmaceutical composition according to claim
 3. 